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Homework Help: Help with Work-Energy

  1. Oct 24, 2004 #1
    I've been working on a problem and I'm stumped :| I'm usually pretty good at deriving the equations for problems and solving them once I find out what I need to be solved. But this one is a bit too ambiguous for me, and I'm looking for a few hints :) Anything is appreciated!

    On an essentially friction-less, horizontal ice rink, a skater moving at 3.0m/s encounters a rough patch that reduces her speed by 45% due to a friction force that is 25% of her weight. Use the work-energy theorem to find the length of this rough patch.

    I've tried a few methods but, alas, no answer. The back of the book says 1.5m if that is of any assistance.

    Thanks again!
  2. jcsd
  3. Oct 24, 2004 #2


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    Just solve the problem using "m" for the mass and it should cancel out in the end.

    You know the initial energy will just be the kinetic energy ([tex]K[/tex]) and that will equal the final kinetic energy plus work done by friction ( [tex]K[/tex]+[tex]W_f[/tex] )
  4. Oct 24, 2004 #3

    I've taken this into consideration, but my answers still end up being too high or too low :(
  5. Oct 24, 2004 #4


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    I worked it out and got 1.46 meters as the answer.

    I said that the final velocity was 3*.45 (although the wording would suggest that it should be 3-(3+.45) but that gives me 1.28)

    Can you show how you're doing it and what answer you get?
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